Foam-filled doors have been manufactured for several years for a variety of uses, e.g., side-hinged entry doors. Such foam-filled doors have advantages over solid wood doors in that foam-filled doors are generally lighter and less expensive, yet can be made to be as aesthetically pleasing as solid wood doors.
In order to decrease the costs of producing doors, manufacturers desire to minimize the materials used in constructing such foam-filled doors. Manufacturers also desire to decrease the amount of time necessary to manufacture the doors. It is further desirable to accomplish the preceding goals while decreasing the percentage of imperfect doors produced in a manufacturing line.
One known method for forming a foam-filled door includes the steps of configuring a frame from rigidly connected rails and stiles; connecting a skin member, or facer, over one side of the frame; applying an even layer of adhesive to the inner side of the facer; inserting pre-formed foam blocks into the frame; and then connecting a second facer over the other side of the frame. More specifically, the frame may be constructed from wood or metal members that are rigidly connected at right angles by screws or other appropriate connecting devices. The facers that are connected to the frame may be formed from a relatively heavy-gauge sheet metal. Increased thickness of the sheet metal helps hide imperfections that would otherwise appear on the outer surface of the door. The pre-formed foam blocks must be accurately sized to prevent the creation of air pockets or voids inside the door which permit moisture collection and reduce insulating characteristics. Another important factor in preventing air pockets is the application of the adhesive to the facers and the foam blocks. The adhesive must be evenly applied and must bond to approximately 100 percent of the facer's inside surface. An even application of adhesive is virtually essential to create a smooth outer surface on the facer. If the adhesive is unevenly applied, surface imperfections will be visible in the outer surface of the facer, and the door will be of inferior quality or a reject. In order to decrease the effect of the adhesive on the facer, heavier-gauge facer plates have been used in the industry. The heavier gauge, however, increases the weight of the door and increases the material cost component of manufacturing the door.
After the adhesive is applied to the inner surface of the first facer and the foam blocks have been inserted according to the subject known method, an adhesive layer is applied to the foam blocks and the inner surface of the second facer. The second facer is then applied to the other side of the frame. Here again, the application of the adhesive in an even layer is important in creating an even bond between the facer and the foam blocks. Perhaps just as important as the even application of the adhesive is the elimination of air pockets in the door. Air pockets are undesirable because they allow moisture to accumulate inside the door, leading to premature deterioration. Air pockets are also undesirable because they detract from the aesthetics of the door by causing bubbles or wrinkles in the facers. Air pockets that occur directly beneath the facer surface allowing the facer to distort are referred to in the art as "oil canning". A further undesirable aspect of this known method is the excessive amount of time necessary to assemble the door.
Another known method of manufacturing a foam-filled door utilizes a poured-in-place process. Such a method generally includes the steps of forming a rigid frame, connecting a pair of facers to each side of the frame, and then pouring or injecting foam into the cavity formed by the frame and the facers. The foam may be relied upon to provide structural support for the door or simply to provide insulation. Problems with this method are that the foaming process often leads to undesirable air pockets that cause doors to be of poor quality or to be rejected. Air pockets are formed when foam is injected into the door, trapping air against the facers and proximate the corners of the frame. These air pockets cause oil canning and lead to moisture accumulation. Another problem is that the foam bond between the frame and the facers is often not strong, leading to eventual delamination and resultant loosening of the facers. One attempt to solve the oil-canning problems in this method has been to use a heavier-gauge facer material. The heavier-gauge material is more resistant to the effects of air pockets but increases the weight and the cost of the doors.